In the past, nitrile rubber has been used as a material for hoses, tubes, and other automobile use rubber parts by taking advantage of its oil resistance, mechanical properties, chemical resistance, etc. Further, nitrile rubber obtained by hydrogenating the carbon-carbon double bonds in the polymer main chain of the nitrile rubber is further excellent in heat resistance, so is used for hoses, seals, and other rubber parts.
In such nitrile rubber, to improve the compression set resistance, for example, Patent Document 1 discloses a cross-linkable rubber composition comprised of a nitrile rubber to which a polyamine cross-linking agent and basic cross-linking accelerator are added. However, in the cross-linkable rubber composition which is described in this Patent Document 1, when obtaining a cross-linked product, there was the problem that if performing steam cross-linking, foaming ended up occurring.